When I was 17 and racing, I rode about 200 miles per week when training. Some of the adult racers would do twice that mileage.

Now at 66 I might do 70 miles a week. It has been enough to lower my heart rate, but plenty of older folks can still ride much farther.

I wasn't cycling for most of my adult life, and took it up again during the pandemic. I think any average would depend a lot on who is deemed a 'cyclist', and how old they are. A set of averages by age groupings would be more interesting to me than one number.